Some integrated circuits include core transistors and input-output (TO) transistors. Core transistors are smaller, occupy less die space, and use a lower supply voltage and lower voltage level signals than IO transistors. In contrast, IO transistors are larger, occupy a larger die space, and use a higher supply voltage and higher voltage level signals.
In some approaches, an input-output (TO) control pin of an integrated circuit uses a voltage level shifter to shift a voltage level of signals for core transistors to a voltage level of signals for IO transistors. Each level shifter in turns uses a native transistor to operate at a low operational core voltage value, such as 1 V. A native transistor is a transistor having a 0 V threshold voltage value. The native transistor occupies about 30% of the total area of a control circuit of the level shifter. A mask used to manufacture the native transistor is expensive.
In some other approaches, a power-on control (POC) circuit is used as an attempt to avoid unknown states of IO pins during power up. The unknown state of the IO pins result in an IO crowbar current and/or a bus contention condition in some situations, such as when a core operational supply voltage is at an operational voltage before an IO operational supply voltage. The level shifter circuit also uses a native transistor, resulting in a larger die area and higher costs compared with a level shifter that does not use the native transistor.
Like reference symbols in the various drawings indicate like elements.